[Attributor] Make use of analysis in the MustBeExecutedExplorer

This commit was made to settle [[ llvm/llvm-project#175 | this issue on GitHub ]].
I added analysis getters for LoopInfo, DominatorTree, and
PostDominatorTree. And I added a test to show an improvement of the
deduction of `dereferenceable` attribute.

Reviewed By: jdoerfert, uenoku

Differential Revision: https://reviews.llvm.org/D76378

Author: okuraofvegetable

llvm/include/llvm/Transforms/IPO/Attributor.h

@@ -107,6 +107,7 @@
 #include "llvm/Analysis/InlineCost.h"
 #include "llvm/Analysis/LazyCallGraph.h"
 #include "llvm/Analysis/MustExecute.h"
+#include "llvm/Analysis/PostDominators.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/CallSite.h"
@@ -566,8 +567,19 @@ struct InformationCache {
   InformationCache(const Module &M, AnalysisGetter &AG,
                    SetVector<Function *> *CGSCC)
       : DL(M.getDataLayout()),
-        Explorer(/* ExploreInterBlock */ true, /* ExploreCFGForward */ true,
-                 /* ExploreCFGBackward */ true),
+        Explorer(
+            /* ExploreInterBlock */ true, /* ExploreCFGForward */ true,
+            /* ExploreCFGBackward */ true,
+            /* LIGetter */
+            [&](const Function &F) { return AG.getAnalysis<LoopAnalysis>(F); },
+            /* DTGetter */
+            [&](const Function &F) {
+              return AG.getAnalysis<DominatorTreeAnalysis>(F);
+            },
+            /* PDTGetter */
+            [&](const Function &F) {
+              return AG.getAnalysis<PostDominatorTreeAnalysis>(F);
+            }),
         AG(AG), CGSCC(CGSCC) {}
 
   /// A map type from opcodes to instructions with this opcode.

llvm/test/Transforms/Attributor/dereferenceable-2.ll

@@ -1,4 +1,5 @@
 ; RUN: opt < %s -attributor --attributor-disable=false -S | FileCheck %s --check-prefix=ATTRIBUTOR
+; RUN: opt < %s -passes=attributor --attributor-disable=false -S | FileCheck %s --check-prefix=ATTRIBUTOR_CGSCC_NPM
 ; Copied from Transforms/InferFunctionAttrs/dereferenceable.ll
 
 ; Determine dereference-ability before unused loads get deleted:
@@ -354,3 +355,47 @@ define void @different_size2(i32* %arg) {
   store double 0.000000e+00, double* %arg-cast
   ret void
 }
+
+; Make use of MustBeExecuted Explorer
+;
+; [CFG]
+; entry
+;  / \
+; l1 l2
+; | X |
+; l3 l4
+;  \ /
+;  l5
+;  / \
+; l6 l7
+;  \ /
+;  end
+; According to the above CFG, we can see that instructions in l5 Block must be executed.
+; Therefore, %p must be dereferenced.
+;
+; ATTRIBUTOR_CGSCC_NPM-LABEL: define i32 @require_cfg_analysis(i32 %c, i32* {{.*}} dereferenceable(4) %p)
+define i32 @require_cfg_analysis(i32 %c, i32* %p) {
+  %tobool1 = icmp eq i32 %c, 0
+  br i1 %tobool1, label %l1, label %l2
+l1:                                       
+  %tobool2 = icmp eq i32 %c, 1
+  br i1 %tobool2, label %l3, label %l4
+l2:  
+  %tobool3 = icmp eq i32 %c, 2
+  br i1 %tobool3, label %l3, label %l4
+l3:
+  br label %l5
+l4:
+  br label %l5
+l5:
+  %tobool4 = icmp eq i32 %c, 4
+  br i1 %tobool4, label %l6, label %l7
+l6:
+  store i32 0, i32* %p
+  br label %end
+l7:
+  store i32 1, i32* %p
+  br label %end
+end:
+  ret i32 1
+}